Method and device for suppressing parasitic effects in a junction-isolation integrated circuit

Abstract

A suppression method is applied to an integrated circuit formed on a substrate of p-type material having at least one region of n-type material with junction isolation, a first electrical contact on the frontal surface of the substrate, a second electrical contact on the n-type region and a third electrical contact on the back of the substrate connected to a reference (ground) terminal of the integrated circuit. To avoid current in the substrate due to the conduction of parasitic bipolar transistors in certain operating conditions of the integrated circuit, the method provides for monitoring the potential of the second contact to detect if this potential departs from the (ground) potential of the reference terminal by an amount greater than a predetermined threshold value. If this occurs the first contact is taken to the potential of the second contact, otherwise they are held at the (ground) potential of the reference terminal. A device and an integrated circuit which utilize the method are also described.

That which is claimed: 
     
       1. A device for suppressing parasitic effects in an integrated circuit formed on a substrate of semiconductor material of a first conductivity type, said device comprising: junction isolation regions;   at least one region of a second conductivity type opposite the first conductivity type, delimited by first portions of a first major surface of the substrate and by said junction-isolation regions;   first electrical contact means with the substrate on second portions of the first major surface outside of said junction-isolation regions;   second electrical contact means on the at least one region of second conductivity type; and   a reference terminal for the integrated circuit;   third electrical contact means on a second major surface of the substrate opposite the first major surface, being connected to the reference terminal of the integrated circuit;   first circuit means connected to said second electrical contact means for monitoring a potential thereof and for detecting if this potential departs from a potential of the reference terminal by an amount greater than a predetermined threshold value; and   second circuit means connected to the first and second contact means and to the first circuit means for connecting the first electrical contact means to the reference terminal if the detected potential is within the predetermined threshold value, and connecting the first electrical contact means to the second electrical contact means if the detected potential is greater than or equal to the predetermined threshold value.   
     
     
       2. A device according to claim 1, wherein said first circuit means comprises a comparator having a first input terminal connected to the reference terminal, a second input terminal connected to the second electrical contact means, and an output terminal functionally connected to the second circuit means. 
     
     
       3. A device according to claim 2, wherein said comparator includes a circuit having first and second branches each including a transistor, and each connected to the other in a current mirror configuration, and wherein the first and second input terminals are connected to the first and second branches, respectively. 
     
     
       4. A device according to claim 1, wherein said second circuit means includes first and second electronic switches which can be activated by the first circuit means on respective control terminals, and which are respectively connected between the first electrical contact means and the reference terminal and between the first electrical contact means and the second electrical contact means. 
     
     
       5. A device according to claim 4, wherein the first and second electronic switches each comprise at least one transistor. 
     
     
       6. A device according to claim 1, wherein the first conductivity type is p, and the second conductivity type is n. 
     
     
       7. A device for suppressing parasitic effects in an integrated circuit formed on a substrate of semiconductor material of a first conductivity type, said device comprising: junction isolation regions;   at least one region of a second conductivity type opposite the first conductivity type, delimited by first portions of a first major surface of the substrate and by said junction-isolation regions;   first electrical contact means with the substrate on second portions of the first major surface outside of said junction-isolation regions;   second electrical contact means on the at least one region of second conductivity type; and   a reference terminal for the integrated circuit;   third electrical contact means on a second major surface of the substrate opposite the first major surface, being connected to the reference terminal of the integrated circuit;   a comparator connected to said second electrical contact means for monitoring a potential thereof and for detecting if this potential departs from a potential of the reference terminal by an amount greater than a predetermined threshold value; and   second circuit means connected to the first and second contact means and to said comparator for connecting the first electrical contact means to the reference terminal if the detected potential is within the predetermined threshold value, and connecting the first electrical contact means to the second electrical contact means if the detected potential is greater than or equal to the predetermined threshold value.   
     
     
       8. A device according to claim 7, wherein said comparator has a first input terminal connected to the reference terminal, a second input terminal connected to the second electrical contact means, and an output terminal functionally connected to the second circuit means. 
     
     
       9. A device according to claim 8, wherein said comparator includes a circuit having first and second branches each including a transistor, and each connected to the other in a current mirror configuration, and wherein the first and second input terminals are connected to the first and second branches, respectively. 
     
     
       10. A device according to claim 7, wherein said second circuit means includes first and second electronic switches which can be activated by said comparator on respective control terminals, and which are respectively connected between the first electrical contact means and the reference terminal and between the first electrical contact means and the second electrical contact means. 
     
     
       11. A device according to claim 10, wherein the first and second electronic switches each comprise at least one transistor. 
     
     
       12. A device according to claim 7, wherein the first conductivity type is p, and the second conductivity type is n. 
     
     
       13. An integrated circuit on a substrate of semiconductor material of a first conductivity type comprising: a plurality of junction-isolation regions;   a plurality of regions of a second conductivity type opposite the first, delimited by first portions of a first major surface of the substrate and by said junction-isolation regions;   first electrical contact means with the substrate on second portions of the first major surface outside of said junction-isolation regions;   second electrical contact means on at least one region of the second conductivity type;   a voltage reference terminal;   third electrical contact means on a second major surface of the substrate, opposite the first major surface, connected to said voltage reference terminal of the integrated circuit;   at least in one region of the plurality of regions of second conductivity type including an electronic switch of a bridge circuit for control of an inductive load, and in which the second electrical contact means provides a first terminal of the electronic switch of the bridge circuit, and a second terminal of the electronic switch of the bridge circuit is connected to the reference terminal;   first circuit means connected to said second electrical contact means for monitoring e potential thereof and for detecting if this potential departs from a potential of the reference terminal by an amount greater than a predetermined threshold value; and   second circuit means connected to the first and second contact means and to the first circuit means for connecting the first electrical contact means to the reference terminal if the detected potential is within the predetermined threshold value, and connecting the first electrical contact means to the second electrical contact means if the detected potential is greater than or equal to the predetermined threshold value.   
     
     
       14. An integrated circuit according to claim 13, wherein said first circuit means comprises a comparator having a first input terminal connected to the reference terminal, a second input terminal connected to the second electrical contact means, and an output terminal functionally connected to the second circuit means. 
     
     
       15. An integrated circuit according to claim 14, wherein said comparator includes a circuit having first and second branches each including a transistor, and each connected to the other in a current mirror configuration, and wherein the first and second input terminals are connected to the first and second branches, respectively. 
     
     
       16. An integrated circuit according to claim 13, wherein said second circuit means includes first and second electronic switches which can be activated by the first circuit means on respective control terminals, and which are respectively connected between the first electrical contact means and the reference terminal and between the first electrical contact means and the second electrical contact means. 
     
     
       17. An integrated circuit according to claim 13, wherein the first and second electronic switches each comprise at least one transistor. 
     
     
       18. An integrated circuit according to claim 16, further comprising a control circuit for the bridge circuit. 
     
     
       19. An integrated circuit according to claim 18, wherein said first circuit means comprises a comparator having an output terminal; and further comprising a logic circuit between the output terminal of the comparator and control terminals of the first and second electronic switches connected to the control circuit of the bridge circuit to synchronize activation of the first and second switches with operation of the bridge circuit. 
     
     
       20. An integrated circuit according to claim 13, wherein the first conductivity type is p, and the second conductivity type is n.